In the real word there are several relationships which can be modeled using a recursive table.
Some examples:
An employee has a manager, which in turn is an employee which has another manager, and so on.
This is modeled with a table like:
EMPLOYEE_ID, MANAGER_ID where EMPLOYEE_ID is the primary key and MANAGER_ID is the foreign key that references to EMPLOYEE_ID
Other examples: a family tree (Father and Sons) or a manufacturing bill of material (Part and sub-components) , etc.
In order to present such tree-like structures it is very useful to have a grid with a link to itself, but SC prevents to create a link from grid A to grid A.
Why this constraint ? Would be possibile to remove it ?